I have signed my C prints and inkjet prints using a fine Sharpie felt-tipped pen. Even under UV Plexi, some of the signatures have faded so badly as to be illegible. Has anyone found a pen that is suitable for this purpose?

Art supply stores carry pens specifically designed for signing artwork. I use a pen from a company called Faber-Castell, that I purchased at my local art dealer. Light Impressions also makes a archival pen that is good for signing prints.

Thank you. It turns out that the Faber-Castell has pigment-based ink so that it does not fade (as much?) with exposure to light. My art supply store also carries a similar product called the Picma pen from Sakura Color Products Corporation which uses archival pigment ink.